Mobile terminals such as a mobile phone, a personal digital assistant (PDA) and the like are driven with rechargeable batteries due to their nature, and the battery of the mobile terminal is charged through supplied electronic energy by using a separate charging apparatus. Typically, the charging device and the battery have separate contact terminals at an exterior thereof, respectively, and are electrically connected with each other by contacting the contact terminals.
However, in such a contact-type charging scheme, the contact terminals protrude outwardly, and thus are easily contaminated by foreign substances. As a result, battery charging is not correctly performed. Further, the battery charging may also not be correctly performed in a case where the contact terminal is exposed to moisture.
Recently, a wireless charging or a non-contact charging technology has been developed and used for electronic devices to solve the above-mentioned problem.
The wireless charging technology uses wireless power transmission and reception, and corresponds to, for example, a system in which a battery is automatically charged if the battery is just put on a charging pad without connecting the mobile phone to a separate charging connector. In general, people know of wireless electric toothbrushes and/or wireless electric shavers as being systems that use the wireless charging technology. The wireless charging technology can improve a waterproof function because it can be used to wirelessly charge the electronic devices. The wireless charging technology can improve the portability of the electronic devices because it does not require a wired charger. Therefore, it is expected that technologies related to the wireless charging technology will be significantly developed in the coming age of electric cars.
The wireless charging technology largely includes an electromagnetic induction scheme that uses a coil, a resonance scheme that uses a resonance, and a radio frequency (RF)/microwave radiation scheme converts electrical energy to a microwave and then transmits the microwave.
Until now, the electromagnetic induction scheme has been considered mainstream, but it is expected that the day will come when all electronic products are wirelessly charged, anytime, anywhere, and without a wire in the near future based on the strength of recent successful experiments for wirelessly transmitting power to a destination that is spaced away by dozens of meters through the use of microwaves at home and abroad.
A power transmission method through the electromagnetic induction corresponds to a scheme of transmitting power between a first coil and a second coil. When a magnet is moved in a coil, induction current occurs. By using the induction current, a magnetic field is generated at a transferring end, and an electric current is induced according to a change of the magnetic field so as to create energy at a reception end. This phenomenon is referred to as the magnetic induction, and the power transmission method using magnetic induction has high energy transmission efficiency.
With respect to the resonance scheme, Prof Soljacic of the Massachusetts Institute of Technology (MIT) announced a system in which electricity is wirelessly transferred using a power transmission principle of the resonance scheme based on a coupled mode theory even if a device to be charged is separated from a charging device by several meters. A wireless charging system of an MIT team employs a concept in physics in which that resonance is the tendency in which when a tuning fork oscillates at a particular frequency, a wine glass next to the tuning fork oscillates at the same frequency. The research team makes an electromagnetic wave containing electrical energy resonate instead of making sounds resonate. It is known that the resonant electrical energy does not affect the surrounding machines and human bodies differently from other electromagnetic waves because the resonant electrical energy is directly transferred only to a device that has a resonance frequency and its unused part is reabsorbed into an electromagnetic field instead of spreading into the air.
Recently, a technology of generating a differential signal and inputting and outputting the differential signal during the process of inputting and outputting power inside the wireless power transmitting apparatus and a wireless power receiving apparatus has been developed. It is possible to improve wireless power transception efficiency and decrease electromagnetic interference (EMI) by using the difference signal.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.